Such an infinitely variable toroidal drive usually has input and output discs coaxially disposed in relation to a common shaft which are arranged in pairs and have toroidal inner surfaces, the same as friction wheels situated between the pairs of input and output discs. The friction wheels are in frictional contact both with the input discs and with the output discs and by friction contact transmit to the output disc the torque transmitted to them by the input disc, the rotational speed of the friction wheels being higher the greater the distance between their point of contact with the input disc and the axis of rotation. By tilting the friction wheels, it is accordingly infinitely and arbitrarily possible to adjust the rotational speed of the output disc. To this end, the axes of rotation of the friction wheels are each mounted on a carrier controllable via a pivoting device.
One such infinitely variable toroidal drive has been described in detail in the Applicant's DE 197 54 725. This drive contains two drive units coaxially disposed relative to the input shaft, each drive unit having one input disc and one output disc between which friction wheels are respectively situated, each friction wheel being fastened on one pivotable carrier. Both input and output discs are mounted upon a torque shaft which is slightly displaceable in an axial direction relative to the input shaft. The input disc of one drive unit is non-rotatably connected with the torque shaft but axially slidingly mounted upon it. The input disc of the other drive unit is also non-rotatably connected with the torque shaft by means of engaging gears. Both output discs of the two drive units are provided in the drive with mirror symmetry side by side and are situated upon a common bushing so that a torque transmitted by one input disc to the appertaining output disc and a torque transmitted by the other input disc to its appertaining output disc is transmitted by the two output discs non-rotatably connected with the bushing to a gear wheel which meshes with a gear wheel of an output shaft. A roller-shaped pressure device energizes one of the input discs which is movably supported in axial direction upon the input shaft and non-rotatably connected therewith.
In the infinitely variable toroidal drives already known, the ratio is usually adjusted by moving the friction wheels tangentially relative to the drive axis, but swiveling forces of the input and output discs act upon the friction wheel situated therebetween, since the former have to be pressed against the friction wheel for transmitting torque. In traditional infinitely variable drives, the friction wheel is placed in each drive unit so that the pivot axis thereof is situated in the central point of the torus defined by the appertaining input and output discs. In the contact points of the friction wheel with the appertaining input disc and output disc, so-called normal forces are generated at the place during adjustment of the ratio.
In the case of dissimilar normal forces appearing during the ratio adjustment, to prevent the implied torque thereby that appears on the friction wheel generates an undesired change of the ratio of the drive, it has already been proposed in the Applicant's DE 198 26 057 to compensate a possible difference of the normal forces by producing a control force and, when the friction wheel is axially retained, said control force, which leads to a rotation of the friction wheel, can be applied to one of the two appertaining discs while, when one of the discs is axially fixed, said control force acts upon the friction wheel.
It has already been proposed to support the friction wheels in an infinitely variable toroidal drive by connecting rods which counteract the reaction forces that appear. The rotation movement of the friction wheels is made possible here by roller bearings; but this arrangement also has the disadvantage of heavy weight of the toroidal wheel drive and a lack of coupling of the rotation movements of the two carriers placed in a drive unit for the friction wheels.
U.S. Pat. No. 4,934,206 has disclosed an infinitely variable toroidal drive with two drive units wherein, in the first drive unit, two carriers and two friction wheels are placed and likewise, in the second drive unit two carriers and two friction wheels are placed. The carriers are interconnected via a total of four rotary belts; one belt connecting two carriers with each other, and each belt having the shape of an eight, that is, having an intersection axially between the two carriers it connects. By said arrangement of belts, a synchronization is obtained on the movements of the carriers for the friction wheels interconnected by the belts. The belts are located on the lower ends of the carriers in the proximity of the longitudinal axis of the drive and serve exclusively for the synchronization of the appertaining carriers. The same as in the transitional toroidal drives, the upper ends of the carriers are supported on the inner wall of the drive housing by yokes, clamps and bearings.
The problem to be solved by this invention is to improve an infinitely variable toroidal drive in the sense of making both the reaction forces acting upon the friction wheels and a synchronization of the rotary movements of the appertaining carriers possible, at low cost and with a single part.
This problem is solved by the features stated in the single claim.